For creating custom information on labels, such as data or bar codes, or even cash receipts, a common practice has been to coat either paper or plastic substrates with a thermal reactive ink that reacts to the heat from a thermal print-head to create a visible contrast on the substrate material.
With the increasing scrutiny of Bisphenol-A—which is a common ingredient or component of such thermal ink coatings—the current thermal printable papers are under increasing pressure to change the composition of the chemicals that create this color contrast. The current approach with thermally reactive coated papers or labels leaves unreacted chemicals on the substrate surface which can expose the public consumer to doses of chemicals that have been shown to have detrimental side effects particularly in children but also in adults, even at low exposure dosages.
Another problem with thermal-change inks is that the image is not stable. It is common knowledge that with time, faxes, receipts, and labels that are printed with these thermal inks often either fade or go completely dark with aging. This is particularly true if exposed to higher temperatures or sunlight.
U.S. Pat. No. 4,004,065 describes a heat sensitive recording member composed of a support and a heat sensitive layer overlying the support. The heat sensitive layer contains an iron salt of a higher fatty acid and gallic acid as color forming components, a stilbene series fluorescent dye as an unusual color forming inhibitor, and hydroxypropyl cellulose and hydroxypropyl methylcellulose.
U.S. Pat. No. 4,602,265 describes a heat sensitive color-producing multi-layer coating including a first coating layer formed from a base polymeric coating composition comprising a solution of film-forming polymer, a source of polyvalent metallic ions, and at least one fatty acid or derivative thereof; a second coating layer, on the first coating layer, formed from a sensitizing coating composition comprising a solution of organic film-forming polymer, at least one fatty acid or derivative thereof, and a reducing agent selected from catechol, pyrogallol, hydroquinone, diphenyl carbazides, gallic acid esters including ethyl gallate, propyl gallate and lauryl gallate, and derivatives thereof; and a third coating layer, on the second coating layer formed from a base polymeric coating composition as defined above.
U.S. Pat. No. 5,863,859 describes a heat-sensitive recording material suited for use in direct thermal imaging, wherein the recording material includes: (i) a layer (1) containing uniformly distributed in a film-forming water-insoluble resin binder a substantially light-insensitive organic metal salt, preferably a silver salt, and (ii) a layer (2) in direct contact with said layer (1) or in thermal working relationship therewith through the intermediary of a spacer layer (3), characterized in that the layer (2) contains, uniformly distributed in a film-forming water-soluble hydrophilic binder at least one organic reducing agent that is capable of diffusing out of said layer (2) into said layer (1) on heating said recording material, and is coated from an aqueous solution.
U.S. Patent Publication No. 2008/0233290 A1 describes a method of preparing a thermally printable sheet which includes providing a substrate including a base sheet having at least one surface coated with a layer containing a pigment in solid porous particulate form, and, using a printer, printing onto the coated surface of the substrate, a thermal ink which includes a color former, a color developer, which can be bisphenol A, and a sensitizer, characterized in that the sensitizer includes dimethyl terephthalate and the ink also includes at least one pigment. This publication also discloses a thermally printable sheet suitable for use in such a method.
U.S. Patent Publication No 2009/0031921 A1 describes a thermal ink which includes a color former, a color developer and a sensitizer, in which the color former can be 3-dibutylamino-6-methyl-7-anilinofluoran; the color developer can be bisphenol A; and the sensitizer can be dimethyl terephthalate; and the ink also comprises at least one pigment. This ink may be used in thermal papers to reduce unwanted discoloration during storage.
U.S. Pat. No. 6,104,422 describes a sublimation thermal image transfer recording method for thermally forming images on an image-receiving sheet prepared by forming a dye-receiving layer on a substrate. The dye-receiving layer contains a subliminal dye-containing ink, such as C.I. Disperse Yellow, Red, Blue; and a binder resin such as polyvinyl butyral or styrene-maleic acid copolymer.
U.S. Pat. No. 4,415,615 describes a cellular pressure-sensitive adhesive membrane including 15 to 85% voids that does not collapse after being briefly compressed, has remarkably good adhesion on contact with rough surfaces and remarkably good flexibility and conformability at sub-freezing temperatures.
U.S. Pat. No. 5,134,174 describes biaxially oriented microporous polypropylene films made using beta-nucleation and specific processing temperatures. The microporous films are open-celled with a high porosity of 30-40% with average pore size of 200-800 Angstroms.
U.S. Pat. No. 4,975,469 describes oriented porous polypropylene-based films using beta-nucleating agents. The pores have typical diameters ranging from 0.2 to 20 microns and inter-connect with each other and are “open-celled” such that the porous film exhibits a high moisture vapor transmission rate of about 2500-7500 g/m2/day. The beta-crystalline portions are extracted via a solvent to form a porous film.
Canadian patent application No. CA02551526 describes a biaxially oriented white polypropylene film for thermal transfer recording including a polypropylene resin of 30% or higher beta crystal ratio and 140-172° C. melting temperature, in which the biaxially oriented white polypropylene film has substantially non-nucleated voids. A receiving layer is provided on one side of the film for thermal transfer recording in which the receiving layer includes at least one or more kinds of resin selected from polyolefin, acryl-based resin, polyester-based resin, and polyurethane-based resin.